With dwindling petroleum resources, increasing energy prices, and environmental concerns, development of energy efficient biorefinery processes to produce biobased chemicals from renewable, low cost, carbon resources offers a unique solution to overcoming the increasing limitations of petroleum-based chemicals.
One chemical with wide industrial and pharmaceutical uses that could be manufactured using a biorefinery process is gamma-butyrolactone (GBL). The global market demand for GBL has been estimated at 850 million lbs/yr, translating to total sales of $1 billion annually. Gamma-buytrolactone is a colorless, weak odor liquid that is used predominantly as an intermediate in the manufacture of commercially important chemicals such as 1,4-butanediol (BDO), tetrahydrofuran (THF), N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), 2-pyrrolidinone, N-vinylpyrrolidone (NVP), polyvinylpyrrolidone (PVP) and so forth. These chemicals have applications in high performance solvents for electronics, lube oil extraction, magnetic wire coatings, engineering resins, pharmaceutical intermediates, cosmetics, hair spray and high valued polymers. GBL by itself has many uses including as a solvent for paint stripping, degreaser, viscosity modifier for polyurethanes, dispersant for water soluble inks, curing agent for urethanes and polyamides, etchant for metal coated plastics, rubber additive and herbicide ingredient.
Petroleum-based GBL is manufactured by several different chemical processes. For example, it is synthesized by dehydration of gamma-hydroxybutyric acid (GHB), by the reaction of acetylene with formaldehyde or vapor phase hydrogenation of maleic anhydride or succinic anhydride and their esters. The latter two methods are respectively known as the Reppe process and the Davy process. The Reppe process was developed in the 1940's and historically was the first commercial route to making 1,4-butanediol. The process starts by reacting acetylene and formaldehyde together which is then followed by a series of hydrogenation stages to obtain BDO and finally dehydrogenation to generate GBL. The main disadvantages of this process are that the starting reactants are quite hazardous and generally present the manufacturer with handling and environmental challenges. Additionally, acetylene is a relatively expensive starting material.
The Davy Process, developed in the 1990's, uses a multistage process that starts by reacting molten maleic anhydride with methanol to produce monomethyl maleate. Next the monomethyl maleate is converted from mono to dimethyl maleate in the presence of an acid resin catalyst. Using catalytic vapor phase hydrogenation, the dimethyl maleate is converted to dimethyl succinate and then finally through a series of additional reactions to a GBL. The final product is refined to obtain the high purity GBL. Many patents describe the various types of hydrogenation catalysts used to convert maleic anhydride or succinic anhydride to GBL. These include copper chromite (described in U.S. Pat. No. 3,065,243), copper chromite with nickel (U.S. Pat. No. 4,006,165), and mixtures of copper, zinc or aluminum oxides (U.S. Pat. No. 5,347,021) as well as reduced copper and aluminum oxides mixtures (U.S. Pat. No. 6,075,153).
Even with the large number of available hydrogenation catalysts for GBL production, there are deficiencies in catalyst performance which need to be overcome such as yield, selectivity, ease of product recovery and cost.
A need therefore exists to develop new GBL manufacturing processes that address not only improvements in the yield, purity, and cost of the product but also use sustainable starting materials that have a more positive impact on the environment.